The association of risk markers and the prevalence of exercise associated muscle cramps in distance runners

Abstract

Title: The Association Of Risk Markers And The Prevalence Of Exercise Associated Muscle Cramps In Distance Runners Candidate: Izaan de Jager Promoter: Prof. MP Schwellnus Co-promoter: Dr. E Korkie Degree: MSc Sports Science Background: The epidemiology, clinical characteristics, severity and the risk markers associated with exercise associated muscle cramps (EAMC) in runners participating in different race distances have not been studied. Aim of the study: To determine the lifetime prevalence, clinical characteristics, severity, preferred treatment and potential risk markers associated with EAMC in distance runners. Design: Cross-sectional study. Setting: 2012-2015 Two Oceans marathon races (21.1km and 56km), South Africa. Participants: 76654 consenting race entrants. Methods: 106743 runners completed an online pre-race medical screening questionnaire as part of the entry for the 2012-2015 races. 76654 (71.8%) consenting entrants were included in this study (21.1km=47069; 56km=29585). The lifetime prevalence (%), retrospective annual incidence (%) and clinical characteristics (main muscle groups affected, timing of occurrence during a race, severity of EAMC, frequency of complex forms of EAMC, and preferred treatment of EAMC) were compared between 21.1km vs. 56km race entrants. Data are reported as frequency (%; adjusted for sex and age groups) and Risk Ratio (RR) with 95%CIs. Secondly, we apply a multivariate model to report independent risk markers associated with a history of EAMC (hEAMC) (sex, age, training variables, history of chronic disease, allergies, prescription medication use and running injuries) in all entrants and 21.1km and 56km entrants (prevalence risk ratios of hEAMC with 95%CI). Results: The lifetime prevalence (%) of EAMC was significantly higher in the 56km (16.0; 15.5-16.5) compared to 21km race entrants (8.8; 8.5-9.1). The onset of EAMC (%) was significantly more frequent in the first quarter (4.9; 4.3-5.7), second quarter (3.7; 3.2-4.4) and after the race (29.5; 28.1-31.1) among 21.1km race entrants, while the onset in 56km race entrants was more frequent in the third (13.7; 12.7-14.8) and fourth quarter (47.2; 45.6-48.9). Serious EAMC (6.9; 6.2-7.8), EAMC associated with dark urine (2.9; 2.4-3.5) and whole body EAMC (4.1; 3.5-4.7) was reported more frequently in 56km race entrants. Specific independent risk markers associated with hEAMC in 21.1km and 56km runners were: history of GIT disease (PR; 21.1km=1.47, 56km=1.58), history of running injury in last 12 months (PR; 21.1km=1.44, 56km=1.45), history of CVD (PR; 21.1km=1.42, 56km=2.10), history of risk factor for CVD (PR; 21.1km=1.34, 56km=1.45), history of allergies (PR; 21.1km=1.21, 56km=1.40), average slower training speed in last 12 months (PR; 21.1km=1.06, 56km=1.03) and increase years of recreational running (PR; 21.1km=1.05, 56km=1.11). Conclusion: More 56km race entrants report ever suffering from EAMC compared to 21.1km race entrants. The muscle groups affected, time of onset, severity (cramp duration), severity of serious EAMC and effective treatment modalities used to relieve acute muscle cramping differed between 21.1km vs. 56km race entrants. Independent risk markers associated with hEAMC identified in this study are male sex, older age, longer race distances runners, training variables, several chronic diseases, a history of allergies and the use of prescription medications for both 21.1km and 56km race entrants.